cmake: Switch to using FindPython3 CMake module

The FindPythonLib CMake module is deprecated since CMake 3.12 and starting
with CMake 3.27 the module is not provided unless CMP0148 is set to OLD.

To integrate PythonQt in other project, the CMake variables `Python3_LIBRARY`
and `Python3_INCLUDE_DIR` may be set instead of `PYTHON_LIBRARY`, `PYTHON_INCLUDE_DIR`
and `PYTHON_INCLUDE_DIR2`.

Options `Python3_ROOT_DIR`, `Python3_LIBRARY_DEBUG` and `Python3_LIBRARY_RELEASE`
may also be set.

Co-authored-by: Hans Johnson <hans-johnson@uiowa.edu>

Author: 2 people

CMakeLists.txt

@@ -43,8 +43,7 @@ set(qtlibs
 #-----------------------------------------------------------------------------
 # Python libraries
 
-find_package(PythonLibs REQUIRED)
-include_directories("${PYTHON_INCLUDE_DIR}")
+find_package(Python3 COMPONENTS Development REQUIRED)
 
 #-----------------------------------------------------------------------------
 # Build options
@@ -304,7 +303,7 @@ target_include_directories(PythonQt
 
 target_link_libraries(PythonQt
   PUBLIC
-    ${PYTHON_LIBRARY}
+    Python3::Python
     ${QT_LIBRARIES}
   )